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Network+ lab 25 of 27

Troubleshooting 2: IP addressing and DHCP faults

A branch has just been moved onto a new address plan, and almost nothing works. Five layered faults hide behind each other: a relay pointing at the wrong server, a mistyped static route that also breaks DHCP, a scope and a host using the old gateway, and a PC with the wrong subnet mask. You isolate each one with the right tool.

Run this lab

It needs Lite: its 6 nodes are set to 6 vCPU and 4,096 MB in total. That fits the free demo too.

In your workspace: Shared, then CompTIA Network Plus N10-009 guided labs, then 25 - Troubleshooting 2 - IP addressing and DHCP faults

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Level
Advanced
Time
About 70 minutes
Nodes need
6 vCPU, 4,096 MB
Smallest plan
Lite

The scenario

The Harbour Logistics branch has just been migrated to a new address plan. In the old plan, the branch gateway was .254; in the new plan it's R2 at 10.20.20.1. DHCP for the branch is served centrally by R1 at head office. Since the cut-over, the help desk's phone hasn't stopped:

  • PC1 (branch, DHCP) "gets no network at all".
  • H1 (branch, configured by hand from the old instructions) "can only see the branch".
  • PC2 (head office) "can reach the internet but not the branch".
DeviceInterfaceAddressRole
R1Gi0/0 / Gi0/1 / Gi0/210.10.10.1/24 / 10.0.12.1/30 / 192.0.2.1/30HQ router, DHCP server
R2Gi0/0 / Gi0/110.0.12.2/30 / 10.20.20.1/24branch router, DHCP relay
R3Gi0/0, Lo0192.0.2.2/30, 203.0.113.1internet
PC2eth010.10.10.20/24, gateway .1HQ PC (static)
PC1eth0DHCP, from .100branch PC
H1eth010.20.20.50/24, gateway .1branch Linux host (static)

The table shows how things should be. Your job is to find every place where reality differs.

What you’ll practise

  • Use ping, traceroute, show ip route and the DHCP bindings to divide the network into working and broken halves
  • Recognise symptoms of a wrong default gateway and a wrong subnet mask
  • Find a static route that's configured but not installed
  • Troubleshoot DHCP relay end to end, including the server's route back to the relay
  • Fix layered faults one at a time and re-test after each

The tasks

  1. Restore H1 as the user left it
  2. Map what works
  3. H1, the wrong default gateway
  4. PC2, the wrong subnet mask
  5. Head office can't route to the branch
  6. The branch gets no DHCP
  7. Verify and document

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of Troubleshooting 2 - IP addressing and DHCP faults6 nodes and 1 network, 6 links. Every link is listed as text below the diagram.R1R2R3PC2PC1H1Branch-LANGi0/1Gi0/2Gi0/0eth0eth0Gi0/0eth0Gi0/1Gi0/0
6 nodes and 1 network, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • R1 Gi0/0 to PC2 eth0
  • R1 Gi0/1 to R2 Gi0/0
  • R1 Gi0/2 to R3 Gi0/0
  • R2 Gi0/1 to Branch-LAN (network)
  • PC1 eth0 to Branch-LAN (network)
  • H1 eth0 to Branch-LAN (network)
Nodes in Troubleshooting 2: IP addressing and DHCP faults, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
R1Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 512 MB
R2Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 512 MB
R3Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 512 MB
PC2VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
PC1VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
H1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder CompTIA Network Plus N10-009 guided labs.

  3. Open 25 - Troubleshooting 2 - IP addressing and DHCP faults and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of CompTIA, Cisco and Netgate. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.